פירוש על עבודה זרה 49:7

That the sun stood still for Joshua is in the Bible itself. There is an unrecorded oral tradition that the sun stood still for Nakdimon b. Gorion, a wealthy member of the elite in Jerusalem around the time of the destruction of the Temple. Rashi says it refers to an instance in Taanit 19b where Nakdimon borrowed 18 springs for the pilgrims to Israel to use. When the time came to pay back the water, and the springs were empty, a miracle occurred and the heavens opened and water filled up the springs. But the king who loaned him the springs claimed that Nakdimon was late and that the day ended without him paying back his debt. Nakdimon prayed and the clouds departed and they saw that it was day.

The amoraim here try to prove that the sun stood still for Moses. The first two amoraim learn this through an exegetical trick called a “gezerah shavah.” This is when the same word appears in two contexts and they say that information stated in one context could also apply to the other.
The third amora learns it from his analysis of the verse itself. He assumes that people would have trembled in front of Moses only if he performed something truly awesome, such as getting the sun to stand still.